Run the audiobooks file scan on an IO thread.

This will allow triggering the scan directly from the UI without
blocking it.

app/src/main/java/com/studio4plus/homerplayer/ApplicationModule.java

@@ -5,9 +5,12 @@
 import android.content.SharedPreferences;
 import android.content.res.Resources;
 import android.net.Uri;
+import android.os.Handler;
+import android.os.HandlerThread;
 import android.preference.PreferenceManager;
 
 import com.studio4plus.homerplayer.analytics.AnalyticsTracker;
+import com.studio4plus.homerplayer.concurrency.BackgroundExecutor;
 
 import java.util.Locale;
 
@@ -64,4 +67,12 @@ EventBus provideEventBus() {
     AnalyticsTracker provideAnalyticsTracker(GlobalSettings globalSettings, EventBus eventBus) {
         return new AnalyticsTracker(globalSettings, eventBus);
     }
+
+    @Provides @Singleton @Named("IO_EXECUTOR")
+    BackgroundExecutor provideIoExecutor(Context applicationContext) {
+        HandlerThread ioThread = new HandlerThread("IO");
+        ioThread.start();
+        Handler ioHandler = new Handler(ioThread.getLooper());
+        return new BackgroundExecutor(new Handler(applicationContext.getMainLooper()), ioHandler);
+    }
 }

app/src/main/java/com/studio4plus/homerplayer/concurrency/BackgroundDeferred.java

@@ -0,0 +1,42 @@
+package com.studio4plus.homerplayer.concurrency;
+
+import android.os.Handler;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.Callable;
+
+public class BackgroundDeferred<V> extends BaseDeferred<V> implements Runnable {
+
+    private final @NonNull List<Listener<V>> listeners = new ArrayList<>();
+
+    private final @NonNull Callable<V> task;
+    private final @NonNull Handler mainThreadHandler;
+
+    BackgroundDeferred(@NonNull Callable<V> task, @NonNull Handler mainThreadHandler) {
+        this.task = task;
+        this.mainThreadHandler = mainThreadHandler;
+    }
+
+    @Override
+    public void run() {
+        try {
+            final @NonNull V newResult = task.call();
+            mainThreadHandler.post(new Runnable() {
+                @Override
+                public void run() {
+                    setResult(newResult);
+                }
+            });
+        } catch (final Exception e) {
+            mainThreadHandler.post(new Runnable() {
+                @Override
+                public void run() {
+                    setException(e);
+                }
+            });
+        }
+    }
+}

app/src/main/java/com/studio4plus/homerplayer/concurrency/BackgroundExecutor.java

@@ -0,0 +1,23 @@
+package com.studio4plus.homerplayer.concurrency;
+
+import android.os.Handler;
+import android.support.annotation.NonNull;
+
+import java.util.concurrent.Callable;
+
+public class BackgroundExecutor {
+
+    private final @NonNull Handler mainThreadHandler;
+    private final @NonNull Handler taskHandler;
+
+    public BackgroundExecutor(@NonNull Handler mainThreadHandler, @NonNull Handler taskHandler) {
+        this.mainThreadHandler = mainThreadHandler;
+        this.taskHandler = taskHandler;
+    }
+
+    public <V> SimpleFuture<V> postTask(@NonNull Callable<V> task) {
+        BackgroundDeferred<V> deferred = new BackgroundDeferred<>(task, mainThreadHandler);
+        taskHandler.post(deferred);
+        return deferred;
+    }
+}

app/src/main/java/com/studio4plus/homerplayer/util/SimpleDeferred.java → app/src/main/java/com/studio4plus/homerplayer/concurrency/BaseDeferred.java

@@ -1,4 +1,4 @@
-package com.studio4plus.homerplayer.util;
+package com.studio4plus.homerplayer.concurrency;
 
 import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
@@ -8,11 +8,11 @@
 
 /**
  * A straightforward implementation of SimpleFuture.
- * It's intended of use only on a single thread.
+ * It's intended for use only on a single thread.
  *
  * Note: I don't need the full power of ListenableFutures nor Rx yet.
  */
-public class SimpleDeferred<V> implements SimpleFuture<V> {
+public class BaseDeferred<V> implements SimpleFuture<V> {
 
     private final @NonNull List<Listener<V>> listeners = new ArrayList<>();
     private @Nullable V result;
@@ -32,15 +32,15 @@ public void removeListener(@NonNull Listener<V> listener) {
         listeners.remove(listener);
     }
 
-    public void setResult(@NonNull V result) {
+    protected void setResult(@NonNull V result) {
         this.result = result;
         for (Listener<V> listener : listeners)
             listener.onResult(result);
     }
 
-    public void setException(@NonNull Throwable exception) {
+    protected void setException(@NonNull Throwable exception) {
         this.exception = exception;
         for (Listener<V> listener : listeners)
             listener.onException(exception);
     }
-}
+}

app/src/main/java/com/studio4plus/homerplayer/concurrency/SimpleDeferred.java

@@ -0,0 +1,14 @@
+package com.studio4plus.homerplayer.concurrency;
+
+import android.support.annotation.NonNull;
+
+public class SimpleDeferred<V> extends BaseDeferred<V> {
+
+    public void setResult(@NonNull V result) {
+        super.setResult(result);
+    }
+
+    public void setException(@NonNull Throwable exception) {
+        super.setException(exception);
+    }
+}

app/src/main/java/com/studio4plus/homerplayer/util/SimpleFuture.java → app/src/main/java/com/studio4plus/homerplayer/concurrency/SimpleFuture.java

@@ -1,4 +1,4 @@
-package com.studio4plus.homerplayer.util;
+package com.studio4plus.homerplayer.concurrency;
 
 import android.support.annotation.NonNull;
 

app/src/main/java/com/studio4plus/homerplayer/filescanner/FileScanner.java

@@ -0,0 +1,49 @@
+package com.studio4plus.homerplayer.filescanner;
+
+import android.content.Context;
+import android.os.Environment;
+
+import com.studio4plus.homerplayer.ApplicationScope;
+import com.studio4plus.homerplayer.concurrency.BackgroundExecutor;
+import com.studio4plus.homerplayer.concurrency.SimpleFuture;
+
+import java.io.File;
+import java.util.List;
+
+import javax.inject.Inject;
+import javax.inject.Named;
+
+@ApplicationScope
+public class FileScanner {
+    public static final String SAMPLE_BOOK_FILE_NAME = ".sample";
+
+    private final String audioBooksDirectoryPath;
+    private final BackgroundExecutor ioExecutor;
+    private final Context applicationContext;
+
+    @Inject
+    public FileScanner(
+            @Named("AUDIOBOOKS_DIRECTORY") String audioBooksDirectoryPath,
+            @Named("IO_EXECUTOR") BackgroundExecutor ioExecutor,
+            Context applicationContext) {
+        this.audioBooksDirectoryPath = audioBooksDirectoryPath;
+        this.ioExecutor = ioExecutor;
+        this.applicationContext = applicationContext;
+    }
+
+    public SimpleFuture<List<FileSet>> scanAudioBooksDirectories() {
+        ScanFilesTask task = new ScanFilesTask(applicationContext, audioBooksDirectoryPath);
+        return ioExecutor.postTask(task);
+    }
+
+    /**
+     * Provide the default directory for audio books.
+     *
+     * The directory is in the devices external storage. Other than that there is nothing
+     * special about it (e.g. it may be on an removable storage).
+     */
+    public File getDefaultAudioBooksDirectory() {
+        File externalStorage = Environment.getExternalStorageDirectory();
+        return new File(externalStorage, audioBooksDirectoryPath);
+    }
+}

app/src/main/java/com/studio4plus/homerplayer/model/FileSet.java → app/src/main/java/com/studio4plus/homerplayer/filescanner/FileSet.java

@@ -1,4 +1,4 @@
-package com.studio4plus.homerplayer.model;
+package com.studio4plus.homerplayer.filescanner;
 
 import com.google.common.base.Preconditions;